1. Field of the Invention
The present invention relates to a novel marine bacterium of metabolizing 3,6-anhydro-L-galactose (3,6-L-AHG) and use of the same.
2. Discussion of Related Art
The world is currently facing a global energy security crisis due to increased energy consumption in developing countries as well as the depletion of petroleum resources. Therefore, there is an urgent need for the development of a biofuel which can replace petroleum resources. In this regard, many nations including the U.S., Europe, Brazil, Japan and China have endeavored their efforts to develop biofuels in order to secure various energy resources and cope with global climate change, and a higher level of investment and research and development are expected to continue in the future. With the advent of post-Kyoto Protocol, South Korea is soon expected to become a country to be forced to reduce its carbon dioxide emissions and thus there is an urgent call for the nation for the development of biofuels. Bioethanol is one of biofuels available to replace petroleum resources, its market has been expanding worldwide and is expected to grow about 17.2% annually. For example, the U.S. plans to replace about 20% of its nationwide gasoline consumption with bioethanol by 2020, and many oil companies including BP and Shell and various venture companies have already joined the research on production of the next generation biofuel. Bioethanol has been mainly thought to be produced using food resources and so issue of the scarcity of food resources and increase in food prices has been raised thus necessitating research into the production of biofuels using inedible resources. Inedible biomass resources are largely classified into ligneous biomass and seaweed biomass. For South Korea with a relatively small territory surrounded by water on its three sides, seaweed biomass is more suitable considering its geographical features. Also, South Korea belongs to the top ranking global seaweed producing countries along with China, Japan and North Korea with its annual gross product amounting to 13,754 tons as of 2006. However, there still remains a large amount of room in terms of its utilization (Fisheries Production Statistics, 2006, Agriculture and Fisheries Production Statistics Division Population and Social Statistics Bureau, National Statistical Office, Korea).
The biomass of red algae includes, based on its dry weight, 60% of agar and 20% of cellulose, i.e., being comprised 80% of it as carbohydrates. Agar, the highest content of red algae, consists of agarose and agaropectin. Both polysaccharides have a structure linked by β-1,4 and α-1,3 bonds in which D-galactose and 3,6-anhydro-L-galactose (hereinafter referred to as ‘3,6-L-AHG’) alternate therein (T. Fu and S. M. Kim, Marine Drugs 2010, 8, 200-218). Therefore, galactose which is fermentable in microorganisms and monosaccharides of 3,6-L-AHG which is not well known in the art can be obtained by hydrolyzing these polymers.
There are two known methods to degrade agarose polymers so far: a chemical method to hydrolyze using a strong acid, such as sulfuric acid and hydrochloric acid, and heat; and an enzymatic method to degrade it using agarase, an enzyme which digests agarose. Agaose is degraded using enzymes derived from microorganisms with agar-degrading capability such as Pseudoalteromonas atlantica (L. M. Morrice et al. Eur J. Biochem. 137. 149-154, 1983), Saccharophagus degradans (N. A. Ekborg. Appl Environ Microbiol. 72(5) 3396-3405, 2006), and Alteromonas sp. (J. Wang et al. Appl Microbiol Biotechnol. 71. 833-839, 2006). Agarose-degrading enzymes can be largely divided into three groups: an enzyme that produces oligosaccharides via hydrolysis of the internal bonds of agarose polymers, an enzyme that degrades a polymer or oligosaccharide into a disaccharide (HT. Kim et al. Appl Microbiol Biotechnol. 86. 227-234, 2010), and an enzyme that degrades a disaccharide into a monosaccharide such as D-galactose and 3,6-L-AHG (Lee, S et al. Acta Crystallogr Sect F-Struct Biolo Cryst Commun. 65. 1299-1301, 2009).
Korean Patent Application Publication No. 10-2010-0108241 (titled as “NOVEL ALPHA-NEO AGAROBIOS HYDROLASE AND A METHOD FOR OBTAINING MONOSACCHARIDE USING THE SAME”) discloses a novel α-neoagarobiose hydrolase and a method of obtaining 3,6-L-AHG using the same. These enzymes are derived from S. degradans, Pseudoalteromonas atlantica T6c. Korean Patent Application Publication No. 10-2008-0093525 (titled as “STREPTOMYCES SP. STRAIN (ACCESSION NO. KCTC 11091BP) HAVING THE ALGINATE HYDROLYSIS ACTIVITY, AN ALGINATE LYASE DERIVED FROM THE SAME, AND A TRANSFORMANT PREPARED BY USING A POLYNUCLEOTIDE ENCODING THE ALGINATE LYASE”) discloses Streptomyces sp. with alginate hydrolysis activity, which degrades alginate into saturate alginate oligomer and unsaturate alginate oligomer, alginate lyase produced by Streptomyces sp., and a recombinant enzyme expressed in E. coli by cloning the gene encoding the alginate lyase.
Meanwhile, the greatest disadvantage that results from the production of bioenergy using seaweed biomass is that it has a low yield in ethanol fermentation using seaweed biomass because 3,6-L-AHG that is one of monosaccharides contained in agarose is a non-fermentable sugar. The metabolism for fermenting D-galactose has already been elucidated. However, so far there has been no report on any bacterial strain which can metabolize using 3,6-L-AHG as a single carbon source and thus there has been no remarkable progress on the studies of identifying the metabolic pathway of the material. Therefore, it is essential to identify the metabolic pathway of L-AHG and, based on the same, develop a method for improving the production yield of bioethanol by converting the non-fermentable sugar into a fermentable sugar.